In the operation of a boiler system, fans generally consume more power than any other station auxiliary. Inasmuch as fuel costs have risen sharply in recent years, and the costs of boiler operation depend to a large extent upon the costs of operating the fans, the costs of plant operation have had a corresponding rise.
Recognizing this, most utilities have taken a hard look at how fan energy may be conserved and the costs of boiler operation may be accordingly lowered. As a result, axial flow fans have been found to consume much less power than centrifugal units when operated under conditions commonly encountered in central power stations. Although the first cost of a centrifugal unit may be less than that of an axial flow unit, and although various other advantages of output, service, and control may be attributed to units of the centrifugal type, the fact remains that a significant power savings may be realized through the use of an axial flow primary air fan instead of a centrifugal fan of the usual type. Inasmuch as axial flow fans are more economical to operate than centrifugal fans, it becomes an object of this invention to provide an arrangement that permits the effective use of an axial flow fan for the supply of primary air to a boiler-furnace.